The present invention relates to an energy storage type feeder voltage compensation apparatus and a method of controlling feeder voltage in which a secondary battery is connected to a feeder of an electric railroad via a power converter to absorb surplus power on the feeder and supply power from a secondary battery in response to power demand from power running rolling stocks.
In recent years, in a feeder system for supplying power from a substation to an electric rolling stock, the electric rolling stock utilizes regenerative brake with the object of power saving. This regenerative brake converts kinetic energy of the electric rolling stock to electric energy by using an inverter mounted on the electric rolling stock, regenerates the electric energy to the feeder, and decelerates the electric rolling stock. The electric energy generated by the regenerative brake is consumed as power running energy of other electric rolling stocks. As a result, energy saving in the feeder system can be attained.
If higher electric energy than needed in the neighborhood of the regenerative rolling stock, i.e., surplus regenerative power is generated, however, the voltage at a receiving point on the regenerative rolling stock rises. In the rolling stock, therefore, the brake must be altered from the regenerative brake to mechanical brake for the purpose of overvoltage protection. As a result, not only the electric rolling stock becomes uncomfortable to ride in, but also the power saving in the feeder system is aggravated.
To solve this problem, a method of storing surplus power in an energy storage apparatus and discharging the stored power as energy at the time of power running of the rolling stock is disclosed in JP-A-11-91415.
A control method for a feeder voltage compensation apparatus including an energy storage apparatus and a power converter is disclosed in MEIDEN REVIEW, Vol. 287, 2002, No. 6, pp. 4-7. An electric double layer capacitor is used as the energy storage apparatus. If the feeder voltage exceeds an upper limit value, the energy storage apparatus is charged. If the feeder voltage becomes lower than a lower limit value, the energy storage apparatus is discharged to suppress the variation in feeder voltage. In addition, when the feeder voltage is in a predetermined range, charging and discharging are conducted between the feeder and the energy saving apparatus so as to make the voltage on the electric double layer capacitor constant. As a result, regenerative power is used effectively, and the charging rate of the power saving apparatus is controlled. In addition, stable operation of the device is ensured.
If a secondary battery is used in the power saving apparatus using the technique disclosed in Meiden Periodical Report, Vol. 287, 2002, No. 6, pp. 4-7, however, the internal resistance value of the secondary battery becomes large at low temperatures, and chargeable and dischargeable power is restricted, resulting in a problem of a lowered availability of the device.